Noise detection circuit and semiconductor system using the same

ABSTRACT

A noise detection circuit may include a divider configured to receive a clock signal and a clock bar signal, divide the clock signal and the clock bar signal, and generate a first divided signal and a second divided signal. The noise detection circuit may also include a noise detection reference block configured to reflect a power supply voltage level variation on the first divided signal and the second divided signal, and generate a first reference signal and a second reference signal, and a duty sensing unit configured to generate first duty information and second duty information of the clock signal in response to the first reference signal and the second reference signal. The noise detection circuit may also include a detection unit configured to generate a noise detection signal in response to the first duty information and the second duty information.

CROSS-REFERENCES TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119(a) toKorean application number 10-2014-0036214, filed on Mar. 27, 2014, inthe Korean Intellectual Property Office, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Technical Field

Various embodiments generally relate to a semiconductor circuit, andmore particularly, to a noise detection circuit and a semiconductorsystem using the same.

2. Related Art

A semiconductor circuit performs all operations with the use of a powersupply voltage.

A semiconductor circuit, that uses the power supply voltage, is likelyto have an operation error when there is a sudden variation in the powersupply voltage. This sudden variation in the power supply voltage may becaused by noise. Thus, noise may cause an operation error to occurwithin a semiconductor circuit.

Accordingly, to cope with operation errors caused by noise, it may beimportant to detect noise generation in the power supply voltage.

SUMMARY

In an embodiment, a noise detection circuit may include a dividerconfigured to receive a clock signal and a clock bar signal, divide theclock signal and the clock bar signal, and generate a first dividedsignal and a second divided signal, and a noise detection referenceblock configured to reflect a power supply voltage level variation onthe first divided signal and the second divided signal, and generate afirst reference signal and a second reference signal. The noisedetection circuit may also include a duty sensing circuit configured togenerate first duty information and second duty information of the clocksignal in response to the first reference signal and the secondreference signal, and a detection circuit configured to generate a noisedetection signal in response to the first duty information and thesecond duty information.

In an embodiment, a semiconductor system may include a memory configuredto selectively activate an error detecting function or a noise detectingfunction in response to a control signal, and accordingly, output anerror detection code or a noise detection signal. The semiconductorsystem may also include a memory controller configured to determine anoperation state of the memory and provide the control signal to thememory, and provide a corresponding command to the memory in response tothe noise detection signal.

In an embodiment, a noise detection circuit may include a dividerconfigured to receive a clock signal and a clock bar signal, divide theclock signal and the clock bar signal, and generate a first dividedsignal and a second divided signal, and a detection circuit configuredto generate a noise detection signal with regards the first dividedsignal and the second divided signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representation of a noise detection circuit inaccordance with an embodiment.

FIG. 2 is a circuit diagram representation illustrating the internalconfiguration of the divider illustrated in FIG. 1.

FIG. 3 is a block diagram representation illustrating an example of aconfiguration of the detection circuit illustrated in FIG. 1.

FIG. 4 is a representation of an operation waveform diagram of FIG. 3.

FIG. 5 is a block diagram representation illustrating an example of aconfiguration of the detection circuit illustrated in FIG. 1.

FIGS. 6 is a block diagram representation of a semiconductor system inaccordance with an embodiment.

FIG. 7 is a block diagram representation illustrating the configurationof the memory illustrated in FIG. 6.

FIG. 8 illustrates a block diagram representation of an example of asystem employing the noise detection circuit and/or the semiconductorsystem in accordance with the embodiments discussed above with relationto FIGS. 1-7.

DETAILED DESCRIPTION

Hereinafter, a noise detection circuit and a semiconductor system usingthe same according to the present disclosure will be described withreference to the accompanying drawings through various examples ofembodiments.

Various embodiments may be directed to a noise detection circuit capableof exactly detecting noise generation in a power supply voltage and asemiconductor system using the same.

Referring FIG. 1, a noise detection circuit 100 in accordance with anembodiment may include a divider 200 and a noise detection referenceblock 300. The noise detection circuit 100 may also include a dutysensing circuit 400 and a detection circuit 500.

The divider 200 may be configured to divide a clock signal CLK and aclock bar signal CLKB. Then the divider 200 may generate first andsecond divided signals D1 and D1B using the divided clock signal CLK andclock bar signal CLKB.

The divider 200 may be configured to be activated in response to acontrol signal EDC_EN.

The noise detection reference block 300 may be configured to reflect apower supply voltage level variation on the first and second dividedsignals D1 and D1B, and generate first and second reference signals D2and D2B.

The noise detection reference block 300 may include and use an inverterchain. The inverter chain performs a delay operation for an inputsignal. The delay operation may implement a scheme of repeatedlyinverting the input signal, according to the structural characteristicof the inverter chain. The inverter chain may have a characteristic thatis sensitive to a variation of a power supply voltage (for example, VDD)level. That is to say, since a power supply voltage level variation isreflected on an input signal delay operation, the inverter chain may beused as a noise detection reference.

The noise detection reference block 300 may be configured to delay therespective first and second divided signals D1 and D1B by apredetermined time. The noise detection reference block 300 may alsogenerate the first and second reference signals D2 and D2B, and reflectthe power supply voltage level voltage variation on the operation ofdelaying the first and second divided signals D1 and D1B.

The duty sensing circuit 400 may be configured to generate first dutyinformation A<1:n> and second duty information B<1:n>. The first dutyinformation A<1:n> and second duty information B<1:n> may be generatedin response to the first and second reference signals D2 and D2Breceived by the duty sensing circuit 400.

The first duty information A<1:n> may be the high pulse widthinformation of the clock signal CLK. The second duty information B<1:n>may be the low pulse width information of the clock signal CLK.

The detection circuit 500 may be configured to generate a noisedetection signal NDET. The noise detection signal NDET may be generatedin response to the first duty information A<1:n> and the second dutyinformation B<1:n> received by the detection circuit 500.

Referring to FIG. 2, the divider 200 may include first and secondtransmission gates 210 and 230. The divider 200 may also include firstand second division logics 220 and 240 and an inverter 250.

The inverter 250 may be configured to invert the control signal EDC_EN.Then, the inverter 250 may generate an inverted control signal EDC_ENB.

The first transmission gate 210 may be configured to transmit the clocksignal CLK to the first division logic 220. When the control signalEDC_EN is deactivated (to a logic low), the first transmission gate 210may transmit the clock signal CLK to the first division logic 220.

The first division logic 220 may be configured to divide the clocksignal CLK transmitted through the first transmission gate 210. Then,the first division logic 220 may generate the first divided signal D1.

When the control signal EDC_EN is deactivated, the second transmissiongate 230 may be configured to transmit the clock bar signal CLKB to thesecond division logic 240.

The second division logic 240 may be configured to divide the negativeclock signal CLKB transmitted through the second transmission gate 230.Then, the second division logic 240 may generate the second dividedsignal D1B.

Referring to FIG. 3, the detection circuit 500 may include an adder 510,a second code comparison part 520, and a subtractor 530. The detectioncircuit 500 may also include a first code comparison part 540 and anoutput control part 550.

The subtractor 530 may be configured to generate a first code SUB<1:n>by subtracting the second duty information B<1:n> from the first dutyinformation A<1:n>.

The first code comparison part 540 may be configured to compare a storedfirst reference code with the first code SUB<1:n>. Then the first codecomparison part 540 may generate a duty error determination signal NS.The duty error determination signal NS may be generated by comparing thestored first reference code with the first code SUB<1:n>.

The first code comparison part 540 may be configured to activate theduty error determination signal NS. When the code value of the firstcode SUB<1:n> is equal to or larger than the code value of the storedfirst reference code, the first code comparison part 540 may activatethe duty error determination signal NS.

The adder 510 may be configured to add the first duty information A<1:n>and the second duty information B<1:n>. Then the adder 510 may generatea second code ADD<1:n>.

The second code comparison part 520 may be configured to compare astored second reference code with the second code ADD<1:n>. Then thesecond code comparison part 520 may generate a frequency determinationsignal FS.

The second code comparison part 520 may be configured to activate thefrequency determination signal FS. When the code value of the secondcode ADD<1:n> is equal to or larger than the code value of the storedsecond reference code, the second code comparison part 520 may activatethe frequency determination signal FS.

The output control part 550 may be configured to generate the noisedetection signal NDET. The noise detection signal NDET may be generatedby the output control part 550 in response to the frequencydetermination signal FS and the duty error determination signal NS.

The output control part 550 may be configured to generate the noisedetection signal NDET. The noise detection signal NDET may be generatedby the output control part 550 in response to the activation of thefrequency determination signal FS and the duty error determinationsignal NS.

The output control part 550 may determine that currently generated noiseis a high frequency component, when the frequency determination signalFS and the duty error determination signal NS are activated, and mayactivate the noise detection signal NDET.

That is to say, the output control part 550 may be configured, forexample, to detect high frequency noise and activate the noise detectionsignal NDET.

Additionally, the embodiments may be configured in such a way as not toconsider a frequency characteristic. In these embodiments, the detectioncircuit 500 may be configured by only the subtractor 530 and the firstcode comparison part 540 and may output the duty error determinationsignal NS as the noise detection signal NDET.

The operations of the noise detection circuit 100 in accordance with theembodiments will be described below with reference to FIG. 4.

In an embodiment, noise generation in units of power may be determined,based on the clock signal CLK.

A power supply voltage VDD is applied, and the first divided signal D1is generated by dividing the clock signal CLK.

While a level of the power supply voltage VDD retains in a predeterminedrange of a voltage level, the first reference signal D2 is normallygenerated by delaying the first divided signal D1.

As the level of the power supply voltage VDD suddenly falls due to powernoise, an operation error occurs in the noise detection reference block300 of FIG. 1, and accordingly, the first reference signal D2 isabnormally delayed.

At a time when the code value of the second code ADD<1:n> is equal to orlarger than the code value of the second reference code, the second codecomparison part 520 of FIG. 3 activates the frequency determinationsignal FS.

At a time when the code value of the first code SUB<1:n> is equal to orlarger than the code value of the first reference code, the first codecomparison part 540 of FIG. 3 activates the duty error determinationsignal NS.

At a time when both the frequency determination signal FS and the dutyerror determination signal NS are activated, the output control part 550generates the noise detection signal NDET of a pulse type.

The first duty information A<1:n> is the high pulse width information ofthe clock signal CLK. The second duty information B<1:n> is the lowpulse width information of the clock signal CLK.

The second code ADD<1:n> which is generated by adding the first dutyinformation A<1:n> and the second duty information B<1:n> may be a codewhich defines the frequency of the clock signal CLK. The first codeSUB<1:n> which is generated by subtracting the first duty informationA<1:n> and the second duty information B<1:n> may be a code whichdefines the duty error of the clock signal CLK, that is, the differencebetween the high pulse width and the low pulse width of the clock signalCLK.

Accordingly, when the value of the second code ADD<1:n> is equal to orlarger than the value of the second reference code which is set todefine a high frequency (the value of which may vary according to asemiconductor operating condition), the frequency determination signalFS is activated to define that the clock signal CLK is a high frequencysignal.

When the value of the first code SUB<1:n> is equal to or larger than thevalue of the first reference code which is set to define the duty errorof the clock signal not conforming to the operating condition of asemiconductor circuit, the duty error determination signal NS isactivated.

In the embodiments where the clock signal CLK is a low frequency signal(the value of which may vary according to the operating condition of asemiconductor circuit), power noise may not exert an adverse influenceon the operation of the semiconductor circuit.

Accordingly, in an embodiment, in order to detect high frequency noise,the output control part 550 is configured, for example, to generate thenoise detection signal NDET of a pulse type at a time when both thefrequency determination signal FS and the duty error determinationsignal NS are activated.

An embodiment may be configured in such a way as not to consider afrequency characteristic. In these embodiments, the duty errordetermination signal NS may be outputted as the noise detection signalNDET.

The detection circuit 500 according to an embodiment may be configuredas illustrated in FIG. 5.

The detection circuit 500 may include an adder 510 and a subtractor 530.The detection circuit 500 may also include an operator 560 and a codecomparison part 570.

The adder 510 may be configured to add first duty information A<1:n> andsecond duty information B<1:n>. Then, the adder 5′0 may generate asecond code ADD<1:n>.

The subtractor 530 may be configured to subtract the first dutyinformation A<1:n> and the second duty information B<1:n>. Then, thesubtractor 530 may generate a first code SUB<1:n>.

The operator 560 may be configured to divide the first code SUB<1:n> asa dividend by the second code ADD<1:n> as a divisor, and output aquotient (or result of the division) as a duty error determination codeQS.

The quotient that is obtained by dividing the first code SUB<1:n> as adividend by the second code ADD<1:n> as a divisor, that is, the dutyerror determination code QS, defines to which degree the duty of theclock signal CLK deviates.

The code comparison part 570 may be configured to compare a storedreference code with the duty error determination code QS. Then the codecomparison part 570 may generate the noise detection signal NDET.

The reference code which is stored in the code comparison part 570 maybe set to define the duty error of the clock signal CLK which does notconform to the operating condition of the semiconductor circuit.

Accordingly, when the value of the duty error determination code QS isequal to or larger than the value of the reference code, the codecomparison part 570 activates the noise detection signal NDET.

The noise detection signal NDET generated in this way may be used forcontrolling the operation of another circuit configuration inside thesemiconductor circuit (for example, a memory), and may be provided to anexternal device (for example, a memory controller such as a CPU or aGPU) of the semiconductor circuit such that the external device maycontrol a memory.

As illustrated in FIG. 6, a semiconductor system 600 in accordance withan embodiment may include a memory controller 700 and a memory 800.

The memory controller 700 may include, for example, a CPU or a GPU. Thememory 800 may include, for example, a DRAM, a flash RAM, a PCRAM, andso forth.

The memory controller 700 may be configured to determine the operationstate of the memory 800, and provide a control signal EDC_EN.

The control signal EDC_EN may be a signal for selecting the errordetecting function or the noise detecting function of the memory 800.

The error detecting function is a function whereby the memory 800provides an error detection code EDC to the memory controller 700. Thenoise detecting function is a function whereby the memory 800 provides anoise detection signal NDET to the memory controller 700.

The memory controller 700 may activate (to a high level) or deactivate(to a low level) the control signal EDC_EN to select the error detectingfunction or the noise detecting function of the memory 800.

The memory controller 700 may determine whether the current operationstate of the memory 800 needs the error detecting function or not, andmay generate the control signal EDC_EN.

The memory controller 700 may transmit and receive data DQ to and fromthe memory 800.

The memory controller 700 may provide a clock signal CLK to the memory800.

The memory controller 700 may be provided with the error detection codeEDC or the noise detection signal NDET through an error detection codeEDC pin from the memory 800.

When the noise detection signal NDET is activated, the memory controller700 may determine that the currently detected noise is a degree likelyto exert an influence on communication with the memory 700. When thenoise detection signal NDET is deactivated the memory controller 700 maydetermine that the currently detected noise is a degree unlikely toexert an influence on communication with the memory 700.

When the noise detection signal NDET is activated, the memory controller700 may provide a corresponding command CMD to the memory 800.

At this time, or when the noise detection signal NDET is activated, thecommand provided by the memory controller 700 to the memory 800 mayinclude an interrupt command for temporarily interrupting the operationof the memory 800, a data retransmission command, or the like.

That is to say, when the current noise is serious enough to be equal toor larger than a predetermined value, a probability for an operationerror to occur in the memory 800 is substantial, and accordingly, thereliability of the data provided from the memory 800 may be degraded.

Accordingly, when the noise detection signal NDET is activated, thememory controller 700 may temporarily interrupt data transmission of thememory 800 through the command CMD, or may request data retransmissionif data has been already transmitted.

The memory 800 may activate and deactivate the internal error detectingfunction, according to the control signal EDC_EN. The memory 800 maydeactivate and activate the noise detecting function, according to thecontrol signal EDC_EN.

When the control signal EDC_EN is activated, the memory 800 may activatethe error detecting function and provide the error detection code EDCthrough the EDC pin to the memory controller 700, and may deactivate thenoise detecting function.

When the control signal EDC_EN is deactivated, the memory 800 maydeactivate the error detecting function, and activate the noisedetecting function and provide the noise detection signal NDET throughthe EDC pin to the memory controller 700.

In accordance with the command CMD, which is provided from the memorycontroller 700, the memory 800 may perform data read and writeoperations.

As illustrated in FIG. 7, the memory 800 may include an error detectioncode generation part 810 and a noise detection circuit 100. The memory800 may also include a multiplexing part 820, an inverter 830, and theEDC pin.

The error detection code generation part 810 may be a component elementand may perform the error detecting function. The error detection codegeneration part 810 may be configured to generate the error detectioncode EDC by using data DQ. The error detection code EDC may be generatedin response to the activation of the control signal EDC_EN.

The inverter 830 may be configured to invert the control signal EDC_ENand output an inverted control signal EDC_ENB.

The noise detection circuit 100 may be a component element and mayperform the noise detecting function. The noise detection circuit 100may be configured to generate the noise detection signal NDET by usingthe clock signal CLK. The noise detection signal NDET may be generatedin response to the inverted control signal EDC_ENB.

When the inverted control signal EDC_ENB is activated, that is, in thecases where the control signal EDC_EN is deactivated, the noisedetection circuit 100 generates the noise detection signal NDET by usingthe clock signal CLK.

When the inverted control signal EDC_ENB is deactivated, that is, in thecase where the control signal EDC_EN is activated, the noise detectioncircuit 100 interrupts the operation for generating the noise detectionsignal NDET.

Since the noise detection circuit 100 may use the configurationdescribed above with reference to FIGS. 1 to 5, the detailed descriptionthereof will be omitted.

The multiplexing part 820 may be configured to output the errordetection code EDC or the noise detection signal NDET to the EDC pin inresponse to the control signal EDC_EN.

When the control signal EDC_EN is in an activated state, themultiplexing part 820 outputs the error detection code EDC to the EDCpin. When the control signal EDC_EN is in a deactivated state, themultiplexing part 820 outputs the noise detection signal NDET to the EDCpin.

The semiconductor systems and noise detection circuits discussed aboveare particular useful in the design of memory devices, processors, andcomputer systems. For example, referring to FIG. 8, a block diagram of asystem employing the semiconductor system and/or noise detection circuitin accordance with the embodiments are illustrated and generallydesignated by a reference numeral 1000. The system 1000 may include oneor more processors or central processing units (“CPUs”) 1100. The CPU1100 may be used individually or in combination with other CPUs. Whilethe CPU 1100 will be referred to primarily in the singular, it will beunderstood by those skilled in the art that a system with any number ofphysical or logical CPUs may be implemented.

A chipset 1150 may be operably coupled to the CPU 1100. The chipset 1150is a communication pathway for signals between the CPU 1100 and othercomponents of the system 1000, which may include a memory controller1200, an input/output (“I/O”) bus 1250, and a disk drive controller1300. Depending on the configuration of the system, any one of a numberof different signals may be transmitted through the chipset 1150, andthose skilled in the art will appreciate that the routing of the signalsthroughout the system 1000 can be readily adjusted without changing theunderlying nature of the system.

As stated above, the memory controller 1200 may be operably coupled tothe chipset 1150. The memory controller 1200 may include at least onesemiconductor system and/or noise detection circuit as discussed abovewith reference to FIGS. 1-7. Thus, the memory controller 1200 canreceive a request provided from the CPU 1100, through the chipset 1150.In alternate embodiments, the memory controller 1200 may be integratedinto the chipset 1150. The memory controller 1200 may be operablycoupled to one or more memory devices 1350. In an embodiment, the memorydevices 1350 may include the semiconductor system and/or noise detectioncircuit as discussed above with relation to FIGS. 1-7, the memorydevices 1350 may include a plurality of word lines and a plurality ofbit lines for defining a plurality of memory cell. The memory devices1350 may be any one of a number of industry standard memory types,including but not limited to, single inline memory modules (“SIMMs”) anddual inline memory modules (“DIMMs”). Further, the memory devices 1350may facilitate the safe removal of the external data storage devices bystoring both instructions and data.

The chipset 1150 may also be coupled to the I/O bus 1250. The I/O bus1250 may serve as a communication pathway for signals from the chipset1150 to I/O devices 1410, 1420 and 1430. The I/O devices 1410, 1420 and1430 may include a mouse 1410, a video display 1420, or a keyboard 1430.The I/O bus 1250 may employ any one of a number of communicationsprotocols to communicate with the I/O devices 1410, 1420, and 1430.Further, the I/O bus 1250 may be integrated into the chipset 1150.

The disk drive controller 1450 (i.e., internal disk drive) may also beoperably coupled to the chipset 1150. The disk drive controller 1450 mayserve as the communication pathway between the chipset 1150 and one ormore internal disk drives 1450. The internal disk drive 1450 mayfacilitate disconnection of the external data storage devices by storingboth instructions and data. The disk drive controller 1300 and theinternal disk drives 1450 may communicate with each other or with thechipset 1150 using virtually any type of communication protocol,including all of those mentioned above with regard to the I/O bus 1250.

It is important to note that the system 1000 described above in relationto FIG. 8 is merely one example of a system employing the semiconductorsystem and/or noise detection circuit as discussed above with relationto FIGS. 1-7. In alternate embodiments, such as cellular phones ordigital cameras, the components may differ from the embodimentsillustrated in FIG. 8.

While various embodiments have been described above, it will beunderstood to those skilled in the art that the embodiments describedare by way of example only. Accordingly, the noise detection circuit andthe semiconductor system using the same described herein should not belimited based on the described embodiments.

What is claimed is:
 1. A semiconductor system comprising: a memoryconfigured to selectively activate an error detecting function or anoise detecting function in response to a control signal, andaccordingly, output an error detection code or a noise detection signal;and a memory controller configured to determine an operation state ofthe memory and provide the control signal to the memory, and provide acorresponding command to the memory in response to the noise detectionsignal.
 2. The semiconductor system according to claim 1, wherein thememory is configured to transmit the error detection code or the noisedetection signal to the memory controller through an error detectioncode (EDC) pin.
 3. The semiconductor system according to claim 1,wherein the memory is configured to activate the error detectingfunction in response to activation of the control signal and provide theerror detection code to the memory controller through the EDC pin, anddeactivate the noise detecting function.
 4. The semiconductor systemaccording to claim 1, wherein the memory is configured to deactivate theerror detecting function in response to deactivation of the controlsignal, and activate the noise detecting function and provide the noisedetection signal to the memory controller through the EDC pin.
 5. Thesemiconductor system according to claim 1, wherein the memory comprises:an error detection code generation part, as a component elementconfigured for performing the error detecting function, configured togenerate the error detection code by using data in response to theactivation of the control signal; a noise detection circuit, as acomponent element configured for performing the noise detectingfunction, configured to generate the noise detection signal by using aclock signal in response to deactivation of the control signal; and amultiplexing part configured to output the error detection code or thenoise detection signal to the EDC pin in response to the control signal.6. The semiconductor system according to claim 5, wherein the noisedetection circuit comprises: a divider configured to receive the clocksignal and a clock bar signal, divide the clock signal and the clock barsignal, and generate a first divided signal and a second divided signal;a noise detection reference block configured to reflect a power supplyvoltage level variation on the first divided signal and the seconddivided signal, and generate a first reference signal and a secondreference signal; a duty sensing circuit configured to generate firstduty information and second duty information of the clock signal inresponse to a first reference signal and a second reference signal; anda detection circuit configured to generate the noise detection signal inresponse to the first duty information and the second duty information,and wherein the clock bar signal is generated by inverting the clocksignal.
 7. The semiconductor system according to claim 6, wherein thenoise detection reference block is configured to delay the first isdivided signal and the second divided signal by a predetermined time andgenerate the first reference signal and the second reference signal, andreflect the power supply voltage level variation on the operation ofdelaying the first divided signal and the second divided signal.
 8. Thesemiconductor system according to claim 6, wherein the detection circuitcomprises: a subtractor configured to subtract the first dutyinformation and the second duty information, and generate a first code;and a first code comparison part configured to compare a stored firstreference code with the first code, and generate a duty errordetermination signal.
 9. The semiconductor system according to claim 8,further comprising: an adder configured to add the first dutyinformation and the second duty information and generate a second code;a second code comparison part configured to compare a stored secondreference code with the second code and generate a frequencydetermination signal; and an output control part configured to generatethe noise detection signal in response to the frequency determinationsignal and the duty error determination signal.
 10. The semiconductorsystem according to claim 6, wherein the detection circuit furthercomprises: a subtractor configured to subtract the first dutyinformation and the second duty information, and generate a first code;an adder configured to add the first duty information and the secondduty information, and generate a second code; an operator configured todivide the first code by the second code, and output a result of thedivision of the first code by the second code as a duty errordetermination code; and a code comparison part configured to compare astored reference code with the duty error determination code andgenerate the noise detection signal.